There have been proposed methods using phosphorus as an n-type dopant to form an n layer on an intrinsic semiconductor substrate or a p-type semiconductor substrate, and to form an n+ layer on an n-type semiconductor substrate. Specifically, the following methods are known: a method comprising performing treatment in a mixed gas atmosphere of phosphorus oxychloride, nitrogen, and oxygen, for example, at 800 to 900° C. for several tens of minutes (e.g., Patent Literature 1); and a method comprising forming an n-type diffusion layer with a solution containing a phosphoric salt, such as phosphorus pentoxide (e.g., Patent Literature 2).